1. Field of the Invention
The present invention generally relates to a circuit board having a predetermined circuit pattern, an electronic device including the circuit board, and a method of manufacturing a circuit board.
Priority is claimed on Japanese Patent Application No. 2005-248449, filed Aug. 29, 2005, the content of which is incorporated herein by reference.
2. Description of the Related Art
All patents, patent applications, patent publications, scientific articles, and the like, which will hereinafter be cited or identified in the present application, will hereby be incorporated by reference in their entirety in order to describe more fully the state of the art to which the present invention pertains.
Generally, processes for manufacturing circuit boards may include, but are not limited to, the following three processes. The first process is to design a circuit that is formed over a board, thereby determining design values of a circuit. The second process is to manufacture a circuit board based on the design values. The third process is to carry out a predetermined set of tests for the manufactured circuit board. When any design deficiency of the circuit board is confirmed by the tests, the circuit design is changed to determine new design values of the circuit, followed by the above-described second and third processes. The above-described first to third processes will be repeated until no design deficiency is confirmed by the tests.
In order to make it easy to test the circuit board, the following techniques have been used. In the process of circuit design, a circuit including a zero-ohm resistance is designed. In the test process, the zero-ohm resistance is used to form a short circuit or is used to allow detecting a current across the zero-ohm resistance. The zero-ohm resistance can typically be realized by a relative element that has an extremely low resistance and has a shape similar to a chip resistance or a lead-type resistance.
The zero-ohm resistance is not needed for a circuit configuration. In this point of view, it would be preferable to eliminate or delete the used zero-ohm resistance for carrying out a mass production of the circuit board after the design of the circuit board has been completed. In the opposite point of view, the zero-ohm resistance can be used again to detect any deficiency of the circuit board in the mass production processes. Actually, however, the mass production of the circuit board including the zero-ohm resistance can often be carried out. Japanese Unexamined Patent Application, First Publication, No. 7-86729 discloses a conventional technique for mounting the zero-ohm resistance on the circuit board.
As described above, the mass production of the circuit board, on which the zero-ohm resistance is mounted, is advantageous in view of making it easy to carry out the test of the circuit board, but is disadvantageous in view of increased total cost of the circuit board. The increase of the total cost is caused by an additional cost of the zero-ohm resistance and another additional cost of mounting the zero-ohm resistance on the circuit board. In general, a rate of defective in mounting the zero-ohm resistance is approximately equal to that in mounting a variety of other circuit elements. Increasing the number of the zero-ohm resistance to be mounted on the circuit board can decrease the manufacturing yield of the circuit board.
An alternative proposal can be made for designing the circuit board without using the zero-ohm resistance even the convenience of the test is sacrificed. In this case, however, if any defectiveness of the circuit board occurs, investigating one or more defective portions of the circuit board needs an additional process for cutting a circuit pattern. This additional process can provide a considerable stress to the circuit board. Even if the defective portion was recovered through the additional process, such considerable stress can render the circuit board unavailable.
In view of the above, it will be apparent to those skilled in the art from this disclosure that there exists a need for an improved circuit board, an improved electronic device, and an improved method of manufacturing a circuit board. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.